R1:b1f4a974fe03

Fix two minor breadcrumb issues in Config

Summary:
Fixes T13159. Two issues here:

- When viewing a particular config setting, there's an extra "Config" crumb.
- On the page for a config group, the link to the parent group has an extra "/config/" in it.

Test Plan:
- Viewed a page for a particular setting, no longer saw an extra "Config" crumb.
- Viewed a page for a setting group, clicked parent crumb, got taken to a real page.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13159…